WASHINGTON (Bloomberg) — Insurance companies are competing to sell no-frills health plans to a generation of so-called young immortals, Americans ages 18 to 34 who don't have medical insurance because they doubt they'll need it.Aetna Inc., WellPoint Inc. and about 160 other US insurance providers see future sales growth in these 19 million young adults. The companies are offering policies with monthly premiums of $39 to $160, hundreds less than other plans. Insurers keep costs low by requiring customers to pay as much as $5,000 of their medical bills before coverage kicks in.

WellPoint, the top US provider of individual health plans, may gain the most from the expanding market. Young adults are the fastest-growing segment of the 45 million Americans without medical coverage. If everyone in the group bought a policy, insurers would gain $25 billion in annual sales, said Sheryl Skolnick, an analyst with CRT Capital Group LLC.

"I don't know how any self-respecting, for-profit, shareholder-owned company can leave that kind of market share and profit on the table," said Skolnick, in Stamford, Connecticut.

From 2000 to 2005, individual health policies sold to young adults increased 6.2 percent to 3.8 million, based on US Census data, while the number of people without coverage climbed 24 percent.

The companies pitching plans to the age group include UnitedHealth Group Inc. of Minnetonka, Minnesota, the largest US insurer; WellPoint of Indianapolis; Aetna, of Hartford, Connecticut; and the San Francisco-based non-profit Blue Shield of California. Philadelphia-based Cigna Corp. and Medica, a Minneapolis-based non-profit, plan to join the competition.

Robert A. Nielsen, 25, works in a Salt Lake City consignment store that doesn't offer a health plan. He was uninsured for a year and a half before buying a policy seven months ago from the non-profit Regence Group of Portland, Oregon.

"I've been meaning to get to it for a long time, and finally just enough fear and concern caught up with me," Nielsen said in a telephone interview.

An online search led him to a policy with a $91 monthly premium, a $1,000 deductible and a $3,500 annual limit on out-of-pocket expenses. Nielsen pays $5 for generic prescription drugs and 25 percent of the price for brand-name medicines. An emergency-room visit would cost $75 plus 20 percent of the bill after Nielsen satisfies the deductible.

Marketing to young adults like Nielsen will make a new generation familiar with health insurance, industry executives say.

"They're exactly the people we need in the insurance pools," said Bob Hurley, spokesman for eHealth, an online broker of health insurance, in a telephone interview. "Their money supports those that have higher health care needs."

EHealth of Mountain View, California, says it sold $36.1 million in policies to the age group in 2006, 59 percent of its revenue, up from $23.8 million, or 57 percent, the previous year.